The semiconductor processing industry has made significant progress in recent years in forming ever-smaller minimum device geometries, which has created a need for processes that form very thin films. This development has in turn led to a need for metrology equipment to measure those films. In many process steps, the thickness of the thin films used to form these structures is becoming ever thinner. Gate oxide thicknesses, for example are now typically on the order of 10 to 20 Angstroms thick. One technique for measuring the thickness of such films is known as ellipsometry.
Ellipsometry is a non-contact, nondestructive, optical technique for the characterization of transparent thin films on surfaces. When a surface or interface is struck by polarized light, ellipsometers measure the change in the reflected light's polarization by detecting and quantifying the change in the amplitude ratio (psi) and the change in phase (delta) induced by reflection of light from the surface.
In another trend, the increasing requirements of high-speed and low-power semiconductor devices has resulted in a significant shift away from aluminum conductors and silicon oxide insulators as the dominant metal/insulator combination in semiconductor multi-level metallization technology. Copper and low k dielectric materials are replacing aluminum metallurgy and silicon oxide dielectrics. It is also anticipated that copper metallurgy and low k dielectric materials will dominate the semiconductor integrated circuit designs. One technique for measuring the thickness of metal films is known as photoacoustic film thickness measurement.
Photoacoustic film thickness measurement is a non-contact, nondestructive optical technique for measuring the thickness of single or multi-layer opaque metal films. A photoacoustic thickness measurement system forms two optical beams: an excitation beam used to excite the surface of the film sample periodically, and a probe beam used to sense the reflectivity of the surface of the sample following each pulse from the excitation beam.